The present invention concerns brakes for use on aircraft landing gear. More particularly, but not exclusively, this invention concerns methods of cooling an aircraft brake, particularly the brake pack. The invention also concerns an aircraft brake for use in such methods, a cartridge for use in such a brake and an aircraft landing gear and an aircraft including such brakes.
Modern aircraft, particularly large aircraft, often use hydraulically actuated disc-type brakes on the landing gear. A typical aircraft brake may comprise a brake pack (also known as a heat pack) comprising a plurality of rotors (connected to the moving wheel) and a plurality of stators (connected to the landing gear bogies via a common piston), and a hydraulic system arranged to move the stators into contact with the rotors when a braking command is received. During braking a significant proportion of the kinetic energy of the aircraft is converted into heat energy that leads to a temperature rise in the brake pack.
In contrast to other vehicle types, aircraft brakes must deal with large energy loads during relatively short and infrequent braking events. This is in contrast to, for example, automotive or railway brakes where braking may be happening almost continuously throughout a journey.
Typically, the size of an aircraft brake pack is primarily dictated by the need to maintain the brake pack within a given temperature range during operation. Currently, the size of a brake pack is often dictated by the need to absorb the large amount of energy generated during a Rejected Take Off (RTO). During normal operations (for example standard take off, landing and taxiing operations) the amount of energy that must be dissipated by the brake pack is lower. It would be advantageous to be able to reduce the size (and therefore mass) of the brake pack in order to increase aircraft efficiency, in particular fuel efficiency.
The temperature of an aircraft's brakes may also play a role in determining the minimum turnaround time of an aircraft during normal operation. A certain amount of time may be required between flights in order to allow the brakes to cool after landing and taxiing to the stand. On routes where an aircraft will take off and land several times during a day brake temperature may accumulate over time. It may be necessary to take account of this heat build-up when route planning in order to ensure that sufficient time between flights is allowed to ensure brakes remain within their operating limits. Accordingly, it would be advantageous to be able to reduce, and/or improve control of, brake temperature.
One prior art method of cooling aircraft brakes is to use a recirculating fluid coolant to remove heat from the brake pack. An example of a brake using such a prior art method is the Eaton Airflex Water-Cooled Brake. However, the amount of heat such a system can remove from the brake pack during a relatively short braking event is limited and accordingly such system may have a limited impact on the maximum temperature reached during a braking event. The use of such systems also increases the complexity of the brake assembly. Another prior art method of cooling aircraft brakes employs fans to generate a convective air flow over the brake pack, see for example US 2009/152055 and U.S. Pat. No. 6,615,958. Again, while this method can be useful in increasing the rate of cooling of a brake pack following a braking event, it has less impact on the maximum temperature reached during such a braking event. It would be advantageous to be able to increase the impact of a cooling system on brake temperature during a braking event, and/or to do so in a mechanically simple way.
The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved apparatus and method for heat management in aircraft brake pads.